CAPTCHA
A CAPTCHA1) is an image containing some distorted letters or numbers. A user must provide these letters and numbers when saving a page. The idea is that a automatic Spam bot isn't able to read the image and thus can't spam the Wiki. CAPTCHAs are somewhat controversial because they may make the site inaccessible for certain users (handicapped people, users with textbased Browsers).
Example CAPTCHA image from Wikipedia
External links
- Inaccessibility of CAPTCHA. Alternatives to Visual Turing Tests on the Web. W3C, 23 November 2005
1)
completely automated public Turing test to tell computers and humans apart